Santander bank today urged its 25 million UK customers not to panic after it was caught up in the ­worsening eurozone crisis.

It rushed to reassure account holders their money was safe after branches and call centres were ­inundated by worried savers.

The move came after ratings agency Moody’s downgraded the bank’s credit status and that of its Spanish parent firm.

Another 15 Spanish banks were also downgraded amid concern about their exposure to debts.

Santander UK stressed that it operated as a separate entity, adding: “This ­structure acts as a firewall to prevent problems within one part of the group spreading to other units in the event of financial difficulties.

“This means money raised in the UK stays in the UK.”

A highly-placed source at Santander said: “The chances of Santander UK being stripped bare are zero.”

Its Spanish owners would need approval from City watchdog the Financial ­Services Authority to take money from the UK arm.

And sources at the FSA said this was highly unlikely.

Bosses are privately fuming at rating agency Moody’s downgrading by one notch.

The decision reflects what experts see as a risk that Santander’s parent company could struggle to bail out its UK arm if it ever got into trouble, because of its ­exposure to Spanish ­mortgages and other debts.